The present invention relates to a current sensor using a differential resistor level shift technique.
Current sensors are widely used in various electrical and electronic apparatus to regulate the apparatus. Current transformers and hall devices are common current sensors being used now. The current sensor market is expected to expand greatly in the coming years. This is in part a result of increasing demand for electric automobiles.
Also much effort is being devoted to devising more efficient electrical apparatus that manages its power usage better. For example, if the current sensor indicates that not enough current is being output, a current source can be caused to output more current. Similarly, if too much current is being output, the current source can be caused to output less current. In this way, the apparatus can be made to operate at an optimal level.
FIG. 1 illustrates a typical current sensor that a hall element. The current sensor comprises a magnetic circuit by a C-shaped magnetic core 102 turned around an electric wire 100 and a hall device 104 arranged in the gap of the magnetic core 102.
FIG. 2 illustrates a current sensor that uses a magneto-impedance device whose magnetic permeability changes in response to the external magnetic. The current sensor includes a non-magnetic substrate 140. A magneto-impedance device 142 and a spiral coil 144 are formed on the substrate 140. The opposite ends of the MI device 142 were connected to electrodes 146a and 146b. The magneto-impedance device is formed from a strip of magnetic thin film.
The spiral coil 144 included a left side coil and a right side coil that are connected to each other. The inner end of the left side coil is connected to the electrode 146b, while the inner end of the right side coil is connected to the other electrode 146b. Thus, as the magneto-impedance device 142 is electrically energized, the coil 144 provides an output that can be used to determine the amount of current flow.
The above current sensors are relatively bulky and expensive to manufacture. It would be desirable to provide a current sensor that is less bulky and less expensive to manufacture.